Ron Hines DVM PhD 4/24/04

For the last twenty-five years, it has been standard veterinary practice in the United States to vaccinate ferrets yearly for canine distemper and rabies. Initially, some vets also vaccinated ferrets for feline panleukopenia (FPV, aka feline distemper, feline enteritis) but no cases of feline panleukopenia have, to my knowledge, ever been diagnosed in the United States. Most states require yearly vaccination of ferrets for rabies. I have used only one approved product for rabies vaccination in ferrets, Merial’s Emrab-3. I have never had a bad reaction to this vaccine.

Canine Distemper:

Formulation, names and availability of vaccines are constantly changing. The vaccines that have traditionally prooved safe in ferrets are all produced from the Onderstepoort and Lederle strain of distemper virus.

I stopped using United Vaccines ferret distemper vaccine, Fervac-D because so many animals went into shock after it was given. Call them and ask if they have reformulated the vaccine so it is now safe.
When they do give it, many vets give only a half-dose because it seems to protect the ferret just as well but cause less reactions. There is also rumor that giving the vaccine in the hip is safer than giving it at the shoulder. I know of no rational to support this claim.
The best distemper vaccine for ferrets was Galaxy-D. It was sold by Solvay Corporation. It was not labeled for ferrets because the cost of obtaining FDA approval for use in ferrets was more than the profit they made selling the vaccine. However, Solvay wasn't making enough money selling this vaccine so they sold the patent to Schering-Plough (possibly Fort Dodge).
See if your vet can call these Companies for advice. If none are available at this time, try to find a catalog vaccine that is marketed to mink farmers.
Best wishes,

Please read my companion article, Distemper & Vaccine Reactions In Ferrets. Unvaccinated ferrets are very susceptible to canine (dog) distemper. It is often spread by sneezing or exposure to infected dogs. It has an incubation period of 6-9 days and is almost always fatal in ferrets. The ferrets become depressed, develop a skin rash, nasal and eye discharges and eventually nerve degeneration. There is no successful treatment. Early signs can be mistaken for human influenza to which ferrets are also susceptible. Generally, ferrets receive their first distemper vaccination at 6-8 weeks and a booster vaccination at 10-12 weeks. Some give a third vaccination at 14-16 weeks of age. They are then generally given a yearly distemper booster vaccination.
The most commonly used vaccine for distemper in ferrets was Fervac-M , manufactured by United Vaccines Inc. Unfortunately I saw too many post vaccination reactions and no longer use it. What was worst – for years the Company denied there was a problem with their vaccine. Too many ferrets that received Fervac vaccine develop anaphylactic (shock) reactions in which they collapsed and which require epinephrine, steroids, antihistamines and oxygen (1). Some years ago we used a vaccine manufactured in chicken eggs called Fromm-D. It was manufactured to be extremely mild for use in fox and mink farms. Unfortunately that Company no longer exists. However, Galaxy brand vaccine manufactured by the Schering-Plough Corporation in monkey cells uses this same attenuated (weakened) virus and can be used successfully in ferrets (1). We just don’t have the scientific studies to prove the ferrets are immune. However, I have never seen a case of distemper in a ferret that received Galaxy vaccine. Most recently, the Merial Corporation released it's new PUREVAX ferret distemper vaccine which is a freeze dried product of a synthetic combination of harmless canary pox to which has been added certain genes from canine distemper virus. The vaccine cannot cause canine distemper under any circumstances and its safety and efficacy have been demonstrated by vaccination and challenge testing of susceptible ferrets. Unfortunately it is not completely without the potential for a bad reaction. Pet ferrets appear to be susceptible to post-vaccinal hypersensitivity reactions at a very low incidence of 0.3%. And none of these reactions resulted in death. They all responded to epinephrine, steroids, antihistamines and oxygen. Although the manufacturer recommends that the vaccine be given subcutaneously, I give it intramuscularly, based on a study that found IM injection gave higher immunity levels (2).

Rabies:
Ferrets, as all warm-blooded animals, are susceptible to rabies. This is passed from animal to animal through bites. There is not treatment for rabies – all animals die. We generally give a rabies vaccination at twelve weeks of age and then yearly. I use the only vaccine approved in the United States for ferrets, Emrab-3 also manufactured by the Merial Corporation.

How Vaccines Work:
Vaccines stimulate the immune system to produce antibodies (titer) against a disease organism so that the ferret is protected against various pathogens in its environment. If the immunized ferret is later exposed to the infectious agent, these antibodies react quickly to attack and neutralize the disease. Ferrets also possess “memory” cells that mount a rapid attack against virus and bacteria that they were once exposed to– even when antibody titer is low or undetectable.
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Determining parental immunity levels in ferret kits is expensive and rarely run. So because we do not know just when to vaccinate we give a series of three or four injections so that at least one of them will work. Another problem is that the immune system of young ferrets is sometimes immature and incapable of mounting a good antibody (titer) defense to the vaccines.

Adult Immunizations:
Once we are sure we have a protected ferret kit we need to decide how often we should revaccinate our ferrets to keep immunity at protective levels. Until recently, veterinarians simply gave all ferrets booster shots every year. This is what the vaccine manufacturers suggested. Besides, it brought our clientele back to our animal hospitals yearly, which increased our income and gave us the opportunity to detect other problems early before the owners were aware of them. Most veterinarians do a thorough physical examination on pets at the time of their yearly vaccinations and we often detect problems during these exams. By law, most states require a yearly rabies vaccination for ferrets - even though studies have shown that many of the rabies vaccines we use give us at least three years of protection.

Many veterinarians, myself included, were suspicious that the vaccines we used were giving much longer periods of protection than one year. We knew this because we never saw distemper in ferrets that had been vaccinated - even many years earlier. Part of the problem involves the typical fee structures of veterinary practices. We tend to undercharge for complex surgery and subsidize those procedures with the money we earn on yearly vaccinations. I do not know how this practice came about but it has existed at least since the 1950’s. There was also an incentive for vaccine manufacturers to sell more vaccine if boosters were recommended annually as well as a one-year mindset among the bureaucrats that staff the USDA Center for Veterinary Biologics that dictate vaccination protocols. These are the same deep thinkers that mandate a two-year expiration date on a vial of water.

How Frequently To Immunize:
I know of no scientific studies that have been conducted on length of immunity in ferrets. But for most dogs, cats and other mammals, vaccination induces a serologic response (titer) to both distemper and rabies that lasts for an extended period – in many instances over four years.
Based on these studies I recommend that ferret kits continue to receive the series of vaccinations we currently give and that they then receive booster vaccinations against distemper the following year. After that, vaccination every three years should protect them well. Indoors ferrets, which make up about ninety-five percent of the ferrets I see, need less frequent boosting than ferrets that go out of doors unsupervised or cavort with unkempt dogs. . No two vaccine manufactures produce identical products so you should not assume that the brand your veterinarian uses induces this long an immunity - but I suspect they all protect well over a year. An exception would be ferrets living in large multi-animal household or that are under heavy stress. Stress is known to depress the immune system. Then, of course, the vaccine does not work. Distemper can pass rapidly from carrier dogs and unprotected dogs at animal shelters and groomers. This often occurs before their personnel has a chance to vaccinate them or for incomming ferrets to have time to develop immunity.

There are other risks involved in too frequent vaccinations. For one, the immune system of your ferret is stressed by these shots. Occasional ferrets develop allergic reactions, facial edema, enteritis, lethargy, fevers, pruritis, nausea, coughing. We also suspect that vaccinations can trigger certain autoimmune diseases. Occasionally these reactions are life threatening. Some vaccines (Not Merial) contain many ingredients besides the dried virus. Some of these, antibiotics and adjuvants (enhancers), are implicated in vaccine reactions. In ferrets that have had prior history of vaccine reactions (Other than to United Products) I often do not give yearly vaccinations. I feel the risks outweigh the benefits and write a letter for the owners to this effect. If I am suspicious that a ferret might have a reaction to a particular vaccine I pre-administer antihistamines (Benadryl) and give a minute test dose of 0.05ml. If the ferret is normal thirty minutes after the test dose I give it the remaining one-milliliter. Other ferrets more at risk are those that attend shows, large grooming or boarding facilities. About one tenth of the ferrets I see fall into this higher risk category.

Determining The Need For Booster Vaccinations By Serum Titer:
It is possible for your veterinarian to remove a serum blood sample from your ferret every year and have it tested for antibody (titer) against distemper. Removing blood from a ferret in the quantities necessary for the test is not an easy task nor one without risk. If the antibody is there, the ferret does not need a booster vaccination against that disease. This is a procedure that will become more widely accepted as time goes by. A lot of veterinary laboratories already offer this service http://www.antechdiagnostics.com/. However, obtaining sufficient blood from a ferret for this test can be a risky procedure that I do not recommend.

1) Rosenthal, KL, The Ferret and Rabbit Pharmacy. In Suppl Compend. Contin. Edu. Pract. Vet. Vol 23, No 2A, 2001.
2) Montali, R. Recommendation sheet for Purevax ferret Distemper Vaccine in Exotic Carnivores
National Zoological Park, Washington.2002. http://66.70.134.35/recommendations_for_merial.htm

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